- website of the Acoustic Ecology Institute
newsCommunityResourcesSoundscapesAbout UsJoin Us
aeinews Home

Flurry of articles, reports debunk(?) wind farm noise concerns

Human impacts, News, Science, Wind turbines Add comments

The past week has seen a flurry of new reports and articles that aim to debunk the idea that wind farm noise should be taken seriously as a concern when siting new wind farms.  AEI’s upcoming Wind Farm Noise 2011 report will address the issue in great depth when it’s released in about a week, but for now I wanted to make a few comments about the recent releases.

Two reports came from Canadian environmental groups that advocate expansion of wind energy and are frustrated by local resistance, especially in Ontario.  I share their support for wind energy providing an increasing percentage of our electrical generating capacity, and have little problem with the bulk of these reports; but in each case, I feel that their treatment of noise issues misdirects attention away from the very real problem at the core of the debate: when wind turbines are built closer than a kilometer or so from homes in rural areas, a high proportion of those nearby neighbors experience significant quality of life impacts due to audible turbine noise.

Sierra Club Canada released a 40-page report entitled The Real Truth About Wind Energy, while Environmental Defence published a 16-page overview entitled Blowing Smoke: Correcting Anti-Wind Myths in Ontario. Both reports begin with reassuring reminders that humans have used windmills for 2000 or more years, and evoke the pleasing image of dutch windmills; neither mentions that the nature of the noise coming from modern turbines is dramatically different than these historic designs.  In particular, as wind turbines get taller, they encounter a larger wind speed difference from the bottom to top of their rotation as well as more random air turbulance and fluctuations within the rotor diameter, both of which contribute to the at-times extreme pulsing or knocking quality of modern wind farm noise.  And while both affirm that low-frequency and infrasonic noise levels are moderate (generally below the threshold of average human perception), they don’t acknowledge the complex amplitude modulation that also occurs at these inaudible levels, which leads some low-frequency noise experts to suggest that they are likely to be perceptible at much lower intensities than the classic hearing threshold curves suggest (entirely separate from as-yet-unproven concerns about this affecting health, there’s little doubt it could make it harder to ignore the noise, increasing annoyance and quality of life impacts). The Sierra report goes into greater detail about acoustics, and while the information is largely accurate, they do of course draw from just some sources, and seem a bit too sure of some of their statements:

  • They state definitively that turbine noise does not exceed 40dB beyond 500meters; this is clearly not the case in many situations (it reflects merely an idealized sound attenuation model, not real world experience).
  • Likewise, the Sierra report suggests that aerodynamic noise has been significantly reduced in recent years, while in fact nearly all industrial turbines still produce sound levels of 100-110dB at the source, not much different than in years past. (100dB is roughly equivalent to a leaf blower or loud boom box, mounted high above the surrounding landscape)
  • And while acknowledging that rural ambient sound levels are commonly as low as 20-30dB, they go on to state with unwarranted assurance that turbine noise at the Canadian allowed limit of 40dB would create minimal annoyance; in fact, many jurisidictions limit new noise sources to 6dB over ambient, because data shows that once it reaches 10db louder, it causes widespread complaints. (40dB will often be 15-20dB over night time ambient)
  • Finally, they cite one of the well-known Scandinavian studies of annoyance levels, though the annoyance rates they mention include nearby neighbors who lease land and receive income from turbines.  The same paper states clearly that among non-leaseholders, annoyance spikes to 25% of those hearing 40dB and more.  In addition, this is but one of three studies by this research team; it took place in a location with a mix of rural and surburban locations, and its annoyance rates were lower than those of their purely rural study, which found annoyance rose to 45% at 40dB and over, very much in line with what many rural communities have found in recent years in the US and Canada.

The Environmental Defence report is less detailed, and stresses that noise from wind turbines cannot be clearly linked to any direct health impacts.  They again cite the Swedish data without correcting for rural populations.  To their credit, the ED report repeatedly stresses that those who do experience high levels of annoyance deserve respect, but by minimizing the rate of such disturbance at close ranges to turbines, they gloss over the primary public policy issue: how close should turbines go to homes?

I share ED and Sierra’s goal of expanding wind power generation.  Where i differ with them is that I feel that we should set siting thresholds at distances that insure that those closest are being minimally impacted.  I agree with their assessment that the majority of those living within sight, and occasional earshot, of turbines are doing fine, but the real-world evidence is becoming increasingly clear that in some communities (especially those with a high proportion of residents who are not working farmers/ranchers), turbine noise levels of 40dB cause significant quality of life impacts on a large minority or small majority of the closest residents. This fact should not be glossed over, and is a valid consideration as communities, provinces, and states settle on wind farm siting standards.

In Ontario, setbacks of 500m (1640ft) are the norm; this is designed keep sound to 40dB; in the US, it’s common to have smaller setback or higher dB thresholds, usually 45dB and sometimes 50dB. These will cause even more severe impacts on the closest neighbors.  Two recent in-depth articles have addressed this, from a couple of perspectives.  One, from the Forbes website, takes exception to recent reporting by Tom Zeller about the noise controversy in Vinalhaven, Maine. The author, William Pentland, frames his piece by saying, “I  do not want to trivialize the noise issue, which is a problem for a very small number of people who live in close proximity to the wind farm.”  Indeed it is.  By focusing the rest of his piece on critiques of these people’s experience and legal challenge, he may not trivialize the issue, but he basically ignores it.  He tries to “put this problem in perspective” by saying that  “many of the island residents who live as close or closer than those who have hired an attorney to represent them in regards to the noise issue are far more upset about the prospects of litigation that they are about the noise.”  Yes, a few close neighbors say they aren’t bothered by the noise, but somewhere around half clearly are, and others haven’t volunteered much about their experience, trying to steer clear of the tempest that’s roaring through town like a winter nor’easter. Pentland also highlights that two of the ten litigants challenging the local electrical co-ops handling of the noise issues come from “away,” which inspires many commenters to chime in on this always-ripe theme, neglecting the clear fact that the other eight are full-time residents.  Only a dozen or so year-round homes are within a half mile or so, where most of the noise issues are arising; this is exactly the situation that allows the noise issue to be painted as an issue affecting “a very small number of people,” while failing to raise the obvious next question: why not build them a bit farther away from homes??

The other recent lengthy article comes from Virginia, where wind farms are beginning to sprout.  It’s a very good read, nicely balanced (as indeed Zeller’s NYTimes piece was).  The author visits a community near one of Virginia’s first wind farms, where the closest resident is 3600 feet away from a turbine (this is just about the distance of the most distant of Vinalhaven neighbors who feel drastically impacted; in other words, if the Vinalhaven turbines had been this far from homes, there would have been few if any big problems). At the Virginia wind farm, this closest neighbor says, “to tell you the truth, at night, I like to listen to it.  It’s kind of a swoosh, but it’s pleasant.”  While visiting another neighbor, who lives three-quarters of a mile away, the author notes that the turbines are barely audible (it being the afternoon, not deep in the night, this means that the turbines are likely to be at least 40dB at this distance, much farther than the 1650 feet that Sierra Canada insisted they’d be at that level). The owner there notes that this was a relatively peaceful moment:  “the harder the wind blows, the louder they are,” he said. “Sometimes they will wake you up at night in the wintertime. There have been times when I turned the TV up a little bit” to drown out the noise.  (Note that this is inside the house with the TV already on, again indicating quite a high noise level, compared to projecttions: an inside noise level of at least 40dB, more likely 50dB).

The Environmental Defence report includes the following big-picture observation:

There is no doubt that the building of a wind power facility brings change to where it is located….A big part of the response to this situation must come from better practices by the Ontario government and wind power companies. More community-owned power projects must emerge to spread greater benefits to local communities. Earlier and better consultation with local communities must take place as projects are designed and implemented. Environmental assessments must be robust, and facility siting decisions done well. Communities must be real partners in development.

I would note that robust environmental assessments should include analysis of likely community reactions to noise increases caused by wind turbines, rather than simply noting the predicted noise levels. Such an analysis would look at increases over ambient and  the nature of the local community (working farm/ranch, vacation home, bedroom community, proportion of retired stay-at-home residents, etc., all of which contribute to whether new audible noise is likely to be acceptable to residents).  As with any environmental assessment, the presence of impacts doesn’t preclude going forward; rather, decision makers use this information as they decide what levels of impact are acceptable in the given location.

For more on AEI’s perspective on community responses to wind farm noise, see this column in Renewable Energy World:  this post about last summer’s DOE-sponsored NEWEEP webinar on wind farm noise; and this recent guest column, Wind Farm Noise: Moderate but Often Disruptive

9 Responses to “Flurry of articles, reports debunk(?) wind farm noise concerns”

  1. Lisa Linowes Says:

    Thank you for your reporting above.

  2. M Anderson Says:

    You do know that Vinalhaven WAS a community-based project. I don’t think that will really solve the problems.

  3. Stephen E. Ambrose Says:

    A community noise impact assessment for quiet areas (<30 dBA) would require the turbine noise levels to be less than 35 dBA or even 32 dBA (Pedersen, etal, Driscoll, Hayes etal)

  4. aeinews Says:

    Well, it wouldn’t REQUIRE any particular turbine noise level, but it would provide a sense of likely community responses at various projected sound levels…. I assume the 35/32dB levels you mention are based on a goal of keeping it within 5-6dB of existing quietest ambient, which is of course the recommended increase to minimize negative community reactions (with 10dB generally triggering some strong reactions). But as I understand most environmental impact statements and assessments, they quantify likely impacts, perhaps with a few alternatives with varying levels of impact, and then policy-makers decide where to set the standards along the continuum from absolutely no impact to unacceptable impacts. Certainly, some towns may choose the “no negative noise impact” option, but others may accept some impact. And I recognize that your target level isn’t the extreme “no impact” option, but a modest impact option, since even 5dB over ambient will trigger some reaction, as it will then be audible and the most noise-senstive folks will begin to feel bothered by it.

  5. Bill B Says:

    My community is considering an industrial wind farm. Recently, I visited a site with 20 turbines about 500′ high (150′ blades). More are being built to bring it to 30 turbines. All 20 were slowly turning in a modest breeze, and yet wherever I stood downwind or upwind from the (under the turbine, 500′ from the turbine, 1000′, or 1500′) there was virtually no audible sound except the whoosh of the blades. The sound resembled a commercial jet liner flying overhead at 30,000+ feet. That concerns me as my community is making noise one of the main counters to the installation. Could it be that turbines that are producing electricity create noticably more noise than turbines that are freewheeling? I am confused by this and hope someone can direct me to a scientific study that differentiates the noise level between working turbines producing electricity and those that are freewheeling or turning without producing electricity. Thank you advance for your help.

  6. aeinews Says:

    Hi Bill,
    The noise that bothers many people is indeed the whooshing of the blades; there is no other notable noise except once in a while when a mechanical problem arises. The turbines you heard may not have been moving at their maximum speed (most commonly about 20rpm or a bit faster, so that one blade passes the top (or the tower) about once per second. ut they don’t make more noise when making electricity, though they probably weren’t at their maximum speed or noise output when you visited.

    For some people in quiet rural areas, the constant sound of a jet overhead is bothersome, distracting, etc. Also, it is quite common that the sound pulses; it appears that was not the case while you were there. This also makes it much harder to ignore, and can become like a dripping faucet kind of stimulus. Finally, in high winds, there is often a knocking kind of noise that is probably caused by various wind turbulence across the huge diameter of the blade-swept area; many people (including most in Vinalhaven who are struggling) say the noise is worst in high winter winds.

    It’s great that you went to hear for yourself, though it’s important to keep in mind that any one period of time is usually not representative of the wide variety of noise that can be made. And, it may well be that you are one of the about half the population that generally finds it quite easy to adjust to new noise; the other half is more apt to find this harder to adapt to, with increasing proportions being upset as the noise gets louder.

  7. Lingard Knutson Says:

    This is an important issue – thanks for a reasonable discussion. I am however, concerned with more that human reactions to wind turbine noise. What is happening to the mammals, reptiles, insects etc. who live around the wind farms? Are they also affected by the noise?

  8. aeinews Says:

    There is very little research that looks at concrete effects of wind farm noise, or any terrestrial human noise, on animals. It’s hard to separate out noise impacts from general human activity and habitat fragmentation. A few studies of oil and gas installations (some with noise, some without) have begun to tease out the noise aspects (brief answer: yes, many/most birds avoid the noisy areas, but some prefer them, perhaps because their egg predators are fewer there). What studies we do have seem to suggest that there is a moderate avoidance of wind farms, out to a few hundred kilometers or so; by moderate, i mean not ALL individuals avoid the area, but there are fewer in areas around turbines than in other nearby places with no turbines. In some ways, it seems analogous to the human situation: many animals don’t like the noise, but some don’t seem to mind. Animals are more apt to be able to move a half mile or mile away if they find it more suitable; humans of course, are more rooted in place.

    While in most areas, there is probably plenty of suitable habitat a mile or more from a new wind farm, one situation that sometimes worries me is wind farms built on narrow forested ridges surrounded by farmland; if these “islands” of habitat are rare or far apart, then displacement of animals from them could be more difficult on the animals. In most cases, I suppose the species are healthy as a whole, so the conventional wisdom would be that the loss of a local population is not “biologically significant” and is worth the trade-off for green energy. This may well be; we do need to keep such things in mind, though, and make such choices consciously.

  9. Mark Cool Says:

    In a NASA Technical Paper delivered to the U.S. Department of Energy Wind – HydroOcean Technologies Division (1990), A-weighted sound pressure levels, expressed in dB(A), emphasize higher frequencies and de-emphasizes lower frequencies in evaluating the effects of noise on communities. The more appropriate measure, dB(G), specifically emphasizes lower frequency evaluation. This is a well known characteristic (i.e. low freqs, infrasonic noise and amplitude modulation) of wind turbines. MassDEP guidance is void from addressing this.

    In a study (Measurements on a Wind Turbine Wake: 3D Effects and Bluff Body Vortex Shedding by D. Medici and P.H. Alfredsson [2006]) a feature of the flow behind a turbine is a low-frequency fluctuation, both in the wake and in the air flow outside the wake.

    TV weather forecasts cold fronts and moving masses of low pressure. Bernoulli’s law of pressure accounts for the same weather characteristics of a cold front in the wake area of giant turbines with huge rotor diameters. The effect is it’s own low pressure climate cell, and given the speed and velocities of the propellers turbulence, it’s it’s own miniature tornado.

    Couple cold air being more dense than warm, and that sound waves travel faster and better through a more dense material, the question is “how far will this low pressure bubble, carrying low frequency infrasound travel?”. The effect of a wind turbine wake, may take as many as 16 rotor diameters for the airstream to recover back to the initial free-air?ow (Wind Turbine Wakes Control and Vortex Shedding. Technical Reports from KTH Mechanics Royal Institute by D. Medici [2004]). This represents a 4304 foot circle around the operational Falmouth MA Vestas82 turbines since each individual machine behaves like an omnidirectional source.

    Though not bombarded by the extreme forces of a tornado, doses of mimicked characteristics over a constant and longer duration of time can be harmful. At sufficiently high levels, numerous studies indicate infrasound can be dangerous and create serious health, visual and motor control problems. What levels are actually dangerous? Could this be what?s causing my headaches, my sleepless nights?”

    The Environmental Protection Agency in Denmark has developed criteria for low frequency and infrasound in general (not just for wind turbines) of 85 dB(G), explicitly allowing a 10 dB factor for people more sensitive than the norm. It’s past time Health and Planning boards follow Denmark’s lead!

Leave a Reply